Created: 19 Nov 2018, 1:28 p.m.

Konstantinos Varvagiannis (Other)

PMID: 29276004 reports on 10 unrelated patients with de novo pathogenic missense variants in RHOBTB2. The phenotype in all individuals was compatible with a developmental and epileptic encephalopathy including early-onset seizures, severe intellectual disability, postnatal onset microcephaly (6/10) and movement disorders (8/10).

The variants occured as de novo events and clustered within the BTB-domain encoding region (within and between the 2 BTB domains). Three missense variants were recurrent and/or concerned the same residue (p.Arg483His in 4 individuals, Arg511Gln was reported in 2, and Arg511Trp was was found in another 2 individuals).

Functional studies in HEK293 cells suggested increased abundance of the mutant protein secondary to decreased proteasome degradation. Using Drosophila as a model organism, altered expression of RhoBTB (the single ortholog of the 3 vertebrate paralogs, closest to RHOBTB2) was shown to result in neurological phenotypes. RhoBTB overexpression in particular was associated with increased bang sensitivity (which was not the case or milder in the case if knockdown of this gene) and impaired performance upon the negative geotaxis assay, similar to the human neurological phenotypes. Altered RhoBTB dosage was shown to be associated with impaired dendrite development.

As commented by the authors, these results as well as the clustering of missense variants and the pLI score of 0.51 reported for RHOBTB2 are consistent with altered protein function (due to the missense variants) rather than haploinsufficiency or loss-of-function.

PMID: 29768694 describes 3 additional individuals, all found to harbor de novo missense variants again within the BTB-domain encoding region. Two of the variants had been reported in the previous study (Arg511Gln and Arg483His) while the third was a private one (Arg507Cys). The phenotype was similar to the previous descriptions. Functional studies were suggestive of impaired degradation of the mutant protein by the CUL3 complex although this was not secondary to decreased binding with CUL3.

PMID: 26740508 (cited by the two aforementioned publications) reports briefly on an individual with de novo missense variant in the same region of RHOBTB2 (Asn510Asp) and Rett-like phenotype.

RHOBTB2 is included in gene panels for intellectual disability offered by different diagnostic laboratories.

As a result the gene can be considered for inclusion in the intellectual disability and epilepsy panels as green. Sources: Expert Review, Literature

Created, Added New Source, Set mode of inheritance, Set publications, Set Phenotypes, Set penetrance, Set mode of pathogenicity

Konstantinos Varvagiannis (Other)

gene: RHOBTB2 was added
gene: RHOBTB2 was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: RHOBTB2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: RHOBTB2 were set to 29276004; 29768694; 26740508
Phenotypes for gene: RHOBTB2 were set to Global developmental delay; Intellectual disability; Seizures; Postnatal microcephaly
Penetrance for gene: RHOBTB2 were set to unknown
Mode of pathogenicity for gene: RHOBTB2 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: RHOBTB2 was set to GREEN
gene: RHOBTB2 was marked as current diagnostic

Rating

If promoting or demoting a gene, please provide comments to justify a decision to move it.

Green list criteria

Genes included in a Genomics England gene panel for a rare disease category (green list) should fit the criteria A-E outlined below.

These guidelines were developed as a combination of the ClinGen DEFINITIVE evidence for a causal role of the gene in the disease(a), and the Developmental Disorder Genotype-Phenotype (DDG2P) CONFIRMED DD Gene evidence level(b) (please see the original references provided below for full details). These help provide a guideline for expert reviewers when assessing whether a gene should be on the green or the red list of a panel.

A. There are plausible disease-causing mutations(i) within, affecting or encompassing an interpretable functional region(ii) of this gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).

OR

B. There are plausible disease-causing mutations(i) within, affecting or encompassing cis-regulatory elements convincingly affecting the expression of a single gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).

OR

C. As definitions A or B but in 2 or 3 unrelated cases/families with the phenotype, with the addition of convincing bioinformatic or functional evidence of causation e.g. known inborn error of metabolism with mutation in orthologous gene which is known to have the relevant deficient enzymatic activity in other species; existence of an animal model which recapitulates the human phenotype.

AND

D. Evidence indicates that disease-causing mutations follow a Mendelian pattern of causation appropriate for reporting in a diagnostic setting(iv).

AND

E. No convincing evidence exists or has emerged that contradicts the role of the gene in the specified phenotype.

References

Mode of pathogenicity

Exceptions to loss of function

It’s assumed that loss-of-function variants in this gene can cause the disease/phenotype unless an exception to this rule is known. We would like to collect information regarding exceptions. An example exception is the PCSK9 gene, where loss-of-function variants are not relevant for a hypercholesterolemia phenotype as they are associated with increased LDL-cholesterol uptake via LDLR (PMID: 25911073).

If a curated set of known-pathogenic variants is available for this gene-phenotype, please contact us at [email protected]

Terms

We classify loss-of-function variants as those with the following Sequence Ontology (SO) terms:

Current diagnostic

If you are submitting this evaluation on behalf of a clinical laboratory please indicate whether you report variants
in this gene as part of your current diagnostic practice by checking the box

Mode of inheritance

Standardised terms were used to represent the gene-disease mode of inheritance, and were mapped to commonly used terms from the different sources. Below each of the terms is described, along with the equivalent commonly-used terms.

MONOALLELIC, autosomal or pseudoautosomal, not imprinted

A variant on one allele of this gene can cause the disease, and imprinting has not been implicated.

A variant on the maternally-inherited allele of this gene can cause the disease, if the alternate allele is imprinted (function muted).

MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown

A variant on one allele of this gene can cause the disease. This is the default used for autosomal dominant mode of inheritance where no knowledge of the imprinting status of the gene required to cause the disease is known. Mapped to the following commonly used terms from different sources: autosomal dominant, dominant, AD, DOMINANT.

BIALLELIC, autosomal or pseudoautosomal

A variant on both alleles of this gene is required to cause the disease. Mapped to the following commonly used terms from different sources: autosomal recessive, recessive, AR, RECESSIVE.

BOTH monoallelic and biallelic, autosomal or pseudoautosomal

The disease can be caused by a variant on one or both alleles of this gene. Mapped to the following commonly used terms from different sources: autosomal recessive or autosomal dominant, recessive or dominant, AR/AD, AD/AR, DOMINANT/RECESSIVE, RECESSIVE/DOMINANT.

BOTH monoallelic and biallelic, autosomal or pseudoautosomal (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal

A variant on one allele of this gene can cause the disease, however a variant on both alleles of this gene can result in a more severe form of the disease/phenotype.

A variant in this gene can cause the disease in males as they have one X-chromosome allele, whereas a variant on both X-chromosome alleles is required to cause the disease in females. Mapped to the following commonly used term from different sources: X-linked recessive.

X linked: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)

A variant in this gene can cause the disease in males as they have one X-chromosome allele. A variant on one allele of this gene may also cause the disease in females, though the disease/phenotype may be less severe and may have a later-onset than is seen in males. X-linked inactivation and mosaicism in different tissues complicate whether a female presents with the disease, and can change over their lifetime. This term is the default setting used for X-linked genes, where it is not known definitately whether females require a variant on each allele of this gene in order to be affected. Mapped to the following commonly used terms from different sources: X-linked dominant, x-linked, X-LINKED, X-linked.

MITOCHONDRIAL

The gene is in the mitochondrial genome and variants within this can cause this disease, maternally inherited. Mapped to the following commonly used term from different sources: Mitochondrial.

Unknown

Mapped to the following commonly used terms from different sources: Unknown, NA, information not provided.

Other - please specify in evaluation comments

For example, if the mode of inheritance is digenic, please indicate this in the comments and which other gene is involved.